International Journal for Research in Engineering Application & Management (IJREAM) ISSN : 2454-9150 Vol-04, Issue-09, Dec 2018 Importance of remotely sensed data to analyze the changing fluvio- geomorphological environment of the uninhabited islands in Indian : special reference to Ajmalmari islands Dr Jayanta Gour Department of Geography, Sambhu Nath College, Labpur, Birbhum, . [email protected]

Abstract - Lots of researches have been done or being carried on the geographical or socio-economic issues of Indian Sundarbans. Even though, due to the restricted entrance to the uninhabited mangrove islands and unavailability of primary as well as secondary data to carry out a case study or research work, we often depend upon the local people’s statements entered or wonder those mangrove. But with the introduction and availability of the satellite imageries, geographers somehow managed and are achieving more and more unknown facts and figures of the ever-mysterious mangrove islands even of the core areas of Indian Sundarbans. The satellite images help a lot to understand and collect the remotely sensed data which might or may lead lots of interdisciplinary works to explore more unknown wealth of the world’s largest mangrove delta, the Sundarbans.

This article has tried to focus on the changing fluvio-geomorphological environment of the uninhabited Ajmalmari Reserve Forest along with the dynamic islands and mid-channel bars to the west of it. Author also explains the tidal dynamics in Indian Sundarbans through RS and GIS which hopefully may help carry on more interdisciplinary research works where both primary and secondary data collection is really a challenging one.

Keywords: Fluvio-geomorphological environment, mangrove, tidal dynamics, Reserve Forest, BOB, Point bar, Mid- channel bar

I. INTRODUCTION obstacle to analyze the spatio-temporal changes in the fluvio-geomorphological environment all over the There are total 101 islands (both habited and uninhabited) Sundarbans. Thus, geographers or scholars from different in IndianSundarbans. As per the delineation line drawn by disciplines have to depend upon the tertiary data or say the Dampier and Hodges, the Indian Sundarbanconsists of remotely sensed data to analyze and interpret the thirteen C.D. Blocks from 24 Pgs.(S)– (9), geomorphological processes acting behind the changing Basanti(2), Canning-I & II(1),(5),Sagar(2) nature of this region controlled by the tidal channels, khals (2), (13), Mathurapur-I(1), and creeks. So, the periodic satellite imageries of this Mathurapur-II(2), (1), Joynagar-I &II (in Kultali) region sometimes become the most important databank to and six C.D. Blocks from 24 Pgs. (N) – Minakhan(1), the geographers by which the fluvio-geomorphological Haroa(5), Sandeshkhali-I(1), Sandeshkhali-II(6), attributes can be quantified and can also be analyzed Hasnabad(1), Hingalganj(2). The numbers within the through different morphometric techniques. The Ajmalmari parentheses denote the inhabited islands in each block islands under the administrative control of the Ajmalmari falling under each region of Indian Sundarbans. Whereas, Reserve Forest area are also a model area where lots of rest 47 islands are still, for god sake has been left as changes have been rectified which also can represent the uninhabited ones. natural dynamism of the intangible tides and bores Almost all the present inhabited islands are either falling in occurring all time modifying the exclusive estuarine deltaic the mature zone or in maturing or say active estuarine zone scenarios of the Indian Sundarbans. of the prograding Delta, the largest in the world. Objectives: Since historical past, many controversies aroused regarding the formation of this Sundarban delta and still now I. To find out the locational significance of the study scholarly researches from different disciplines are going on area. to search the ground reality of the typical formation and II. To acquire, calculate the quantitative as well as degradation of the mangrove islands decades after decades. qualitative data and to analyze the data obtained from But the insufficiency of primary as well as census level data the satellite imageries of the region of interest. related with the uninhabited parts often becomes an

278 | IJREAMV04I0945067 DOI : 10.18231/2454-9150.2018.1190 © 2018, IJREAM All Rights Reserved. International Journal for Research in Engineering Application & Management (IJREAM) ISSN : 2454-9150 Vol-04, Issue-09, Dec 2018

III. To year-wise compare the spatio-temporal changes in II. Digital Classification of the satellite imageries the fluvio-geomorphological attributes of this area. through supervised and unsupervised techniques. IV. To relate the result obtained from the analysis and to III. Extraction of different physical and cultural represent it as a model one in Indian Sundarbans. attributes. IV. Calculating the number (point), Length (line), ETHODOLOGY II. M Area (polygon) of the vector layers.  Pre-Phase:  Post-Phase: I. Literature Review – Mainly scholarly articles I. Comparing the fluvio-geomorphological data related to the physical or geomorphlogical studies extracted both from Toposheets and Satellite on Indian Sundarbans in books and journals have Imageries from 2009 to 2016 (IRS LISS-III been gone through to collect previously published images downloaded from authenticated report about the problem area. https://bhuban.nrsc.gov.in). II. Collection of - NATMO Map, Toposheet No.s - II. Analyzing and Interpreting the data to make them NF 45-8 and NF 45-8 Series U502 with R.F. a secondary source (Through Mapping and 1:250k, F45Q9 and F45K12 with R.F. 1:50k) and articles) to the interdisciplinary research works Satellite Imageries (IRS LISS-III,2009-2016) from where primary and secondary data are not https://www.bhuban.nrsc.gov.in. available.  Phase of Data Processing: Location of the study area: Geographically the study I. Geo-referencing the selected Toposheets (Raster comprises three prominent islands of Indian Sundarbans layers) and digital processing of the different extending between the 88.58˚E to 88.67˚E longitudes and bands in the same CRS through Arc GIS and 21.79˚N to Google Surfer-16 software.

Fig.1: Location of the study area in district of 24 Pgs. (S), , India 21.92˚N latitudes covering an area of ± 74.23 km² land Geomorphologically these are mangrove islands which are area. The islands are mainly delineated by the confluence of the formed due to the continuous deposition of silt and clay Matla River and to the north, Matla River (O’Malley, 2009), by the River Matla and that of the tidal to its east, the Suia Gang, an interlinking tidal channel creeks bearing the saline marine water of Bay of Bengal (between the Dulibhasani Reserve Forest and Ajmalmari (BOB) which is ± 45.71 km (heading 179.74 degree) away Reserve Forest) connecting the Matla River to the from its southernmost tip. It has a very typical estuarine Ajmalmari-Kankalmari Rivers to the south and the locational significance in the central part of the prograding Ajmalmari River, Kankalmari Rivers to its west. Indian side Sundarban Delta.

279 | IJREAMV04I0945067 DOI : 10.18231/2454-9150.2018.1190 © 2018, IJREAM All Rights Reserved. International Journal for Research in Engineering Application & Management (IJREAM) ISSN : 2454-9150 Vol-04, Issue-09, Dec 2018

Administratively this mangrove islands fall under the average temperature is 25˚C-30˚C with maximum of 40˚C administrative jurisdiction ofKultali C.D. Block in South 24 in summer (May/June) and minimum of 10˚C. The three Parganas, West Bengal. The study area covers about mangrove islands experience an average annual rainfall 24.24% area of the total block area (306.2km²). The islands between1200 mm to 1900 mm. The nearness to Bay of of Gosaba and Basanti C.D. Blocks lie to the east to the Bengal and frequent formation of depression, cyclone and north respectively. These islands are still the uninhabited cyclonic storms sometimes play a major role in the tidal ones and are under the control of the Ministry of Sundarban water level and temporarily accelerate the riverine Affairs, Govt. of West Bengal. So, it is also having an activities. Closeness to the BOB keeps the relative humidity administrative importance as these are uninhabited but a more than 80% during the wet season (March-September) tourist attraction also. The three island compartments under and 50-70% during dry season (October-February). the Ajmalmari Reserve Forest used to serve as the steamer In general these three islands are made up of fine silt and signaling area during the British colonial period in Bengal. clay with finer alluvium. The tide water laden suspended The SOI Toposheets of 1924 of this region (NF45-08 and load often help in the formation of point and mid-channel NF45-12, SERIES U-502) reveal the fact that this area had bars around the islands and along the tidal channels and four Steamer Signals, particularly at the confluences of creeks draining them twice a day. Kankalmari River and Sindurkati Khal, at the confluence of Kankalmari River and Benifuli Khal and along the right Geological set up the Bengal Delta: Marine transgression bank of Matla River along its northern border (Fig.1). Still on the Bengal shelf occurred locally during late Cretaceous today, these islands are uninhabited and the homeland of and widely during Eocene. During Miocene, only the rare mangrove and endangered animal species. eastern parts of the Bengal shelf were under marine influence.Slow subsidence of the shelf area during late Relief and Climate: The Ajmalmari mangrove islands Cretaceous when brackish to lagoonal deposits accumulated within the specific coordinates as stated earlier are mainly on the Bengal shelf. During Pliocene, with the regression of the active estuarine parts of the Bengal Delta (Indian side) the sea, estuarine and fluvial conditions of deposition and are the tidal riverine depositional products. The prevailed in most parts of the Bengal (Bagchi, 1945). maximum elevation of the islands is ± 5.0 m and minimum ± 0.25 m above MSL (from the DEM Fluvio-geomorphological Environment in Ajmalmari analysisC1_DEM_16B_2006-2008_v1_88E21N_f45q) and Islands in Indian Sundarbans: from the altitudinal analysis by Surfer-16 (Fig.2 & Table 2). The study area as is an estuarine deltaic part of the Indian Sundarbans is mainly of sedimentary depositional landform in origin (Paul, 2005). The sediment load borne by the River Matla and Bidyadhari has been playing a major controlling factor behind the formation of the study area envisaging three major and one minor estuarine deltaic island with some creeks. Besides, settling of the suspended particles, coming from the incoming tidal waves of the Bay of Bengal (BOB) for some decades, also helped or is helping in the accreditation processes particularly in this location. Same locational significances can be correlated to the location of Haliday Island just to the south of these islands (± 45km). Geomorphologically the study area is made up of fine silt and clay with uneven surface although the relative altitude ranges between 0-4.5m in the north Fig.2: Relief Map of the north compartment part of the compartment, 0-5m in the central island part and 0-1m in Ajmalmari-Kankalmari Mangrove Islands (2018) the southern island part. From this, it’s very much clear that this intertidal area is The Relief Map (Fig.2) of the north compartment part very much prone to submergence during the high tides or among the three macro island system of the Ajmalmari- during tidal bores particularly during cyclonic conditions Kankalmari Islands (interfluvial area between Kankalmari when the tidal river water level rises more than 5 m. River-Ajmalmari-Suia Gang and Matla River) also indicate that the contour heights (clamped to ground) are relatively Climatic and Soil Characteristics: The study area is higher in the northern section of the north compartment part located in the central zone of the Indian Sundarbans. So, bordering the Kankalmari River, whereas, the rest portions likewise the climatic condition prevailing over the South 24 (particularly the SE section) are having relatively lower Parganas, West Bengal in India, the Ajmalmari Islands also altitudes. The probable reasons found from the analysis of experience the Tropical Monsoon type of climate mostly the satellite imageries of the said study area are – influenced by the BOB (about ± 45km away). The annual

280 | IJREAMV04I0945067 DOI : 10.18231/2454-9150.2018.1190 © 2018, IJREAM All Rights Reserved. International Journal for Research in Engineering Application & Management (IJREAM) ISSN : 2454-9150 Vol-04, Issue-09, Dec 2018

I. The Matla River after taking the huge amount of at its southern most passage, particularly in the suspended sediment load from Bidyadhari River confluence zone of Kankalmari River-Ajmalmari flow down towards the BOB and bypass through and Matla River. Thus, the zone, just south of the the Kankalmari River-Ajmalmari, a distributary Herobhanga Is., is a meeting of three loads bearing tidal channel of Matla River which actually tidal channels viz. Matla River, Bidyadhari River bifurcates into three interlinking tidal channels and and Kankalmari River-Ajmalmari. The peculiar creeks as following – fluvio-geomorphological environment helped in the formation and aggradation of the Ajmalmari (a)A narrow tidal creek i.e. Olian Nala linking the islands in Indian Sundarbans. Thakuran River to the Matla River III. The abandoning of the Matla River in its via Ajmalmari River and Kankalmari River. catchment area as well as the increase in the (b) A narrow tidal channel viz. Suia Gang, an suspended load year after year have combined interlinking channel between the R. impact over the formation of lots of point and mid- channel bars along both side banks of Matla River Ajmalmari and Matla River, and (Das, 2006). But, as all the tidal rivers flow with (c) Benifuli Khal and Sindurkati Khal, the higher velocity during ebb tides along their right interlinking tidal creeks ply the tidal bank towards the BOB rather than the left banks along which the incoming lighter tidal bore flow dischargeof Kankalmari River, Ajmalmari River with higher velocity, the left banks become least and Matla River (Fig.1). affected by the undercutting processes by the river II. As the Matla Riverstartsnarrowing from the water. Herobhanga Is.(to the east) and Kaikhali Abad (to Besides this, from the digital analysis of the satellite the west) up to Canning and flows down almost in imageries of the study area it has also been found that these linear alignment with sluggish flow during the ebb three islands also passed through spatio-temporal changes tides, so, it accumulates most of the sediment load in areal Table 1: The erosional and depositional activities in Ajmalmari islands (2009 to 2016)

2009 (Year of Base Layer) 2016 (Year of Last Layer) Result Island Remarks Sl. No. Area (km²) Area (km²) Area (km²) Deposited or Eroded Compartments 1 North 14.125607 13.88430781 -0.241297 Loss 2 Middle 38.05688498 38.02678344 -0.03010154 Loss 3 South 15.98951756 16.07012016 +0.0806024 Gain Source: Result from digital processing of the satellite imageries coverage since 2009 to 2016. The spatio-temporal changes in the amount of suspended sediment load in Matla River, Bidyadhari River, Kankalmari River-Ajmalmari, Benifuli Khal, Suia Gang has also shown a shown that there is a loss of 0.241297 km² and 0.03010154 km² land area in the northern and middle islands respectively during this period. Whereas, the southern part among those three islands of Ajmalmari RF area has shown a gain (0.0806024 km²) in areal coverage (Table 1). Although the amount of land and loss is negligible but the factor behind the depositional activities in the southern part (towards the mouth of Matla River) can draw an inference. Hence, it is quite a common phenomenon caused by altering erosional and depositional activities by the shifting tidal channels particularly in the estuarine deltaic zone of the Indian Sundarbans (Mukhopadhyay and Mukhopadhyay, 2005).

281 | IJREAMV04I0945067 DOI : 10.18231/2454-9150.2018.1190 © 2018, IJREAM All Rights Reserved. International Journal for Research in Engineering Application & Management (IJREAM) ISSN : 2454-9150 Vol-04, Issue-09, Dec 2018

Fig.3: Spatio-temporal changes in the fluvio-geomorphological environment in Ajmalmari islands since 2009 to 2016. The reasons behind the maximum loss of land area in the northernmost island as noticeable are – a) Formation of helical flow at the junction of the Matla, Bidyadhari, Kankalmari Rivers around and along the northern part (just south of Herobhanga Is.). The sharp bending and meandering of the Matla River also accelerate the changing erosional and depositional rate depending upon the seasonal amount of discharge

Table 2: The probability (%) of submergence of the Ajmalmari islands during high tides Island compartment Tide Water Level increase/decrease (in m) Submergence (%) under Tidal Waves 0.65m HTW enters North 0.80m 50% 0.96m 99% submerged 0.47m high tide water enters Middle 0.96m 99% submerged South <0.50m 50% submerged Source: Digital analysis with 3D modeling through Google Surfer 16 *BOB- Bay of Bengal, HTW- High tide water

282 | IJREAMV04I0945067 DOI : 10.18231/2454-9150.2018.1190 © 2018, IJREAM All Rights Reserved. International Journal for Research in Engineering Application & Management (IJREAM) ISSN : 2454-9150 Vol-04, Issue-09, Dec 2018

Noticeable changes in the fluvio-geomorphological fluvio-geomorphological environment for the formation of environment in the Ajmalmari islands along Matla River a new stable land area along or within the tidal river beds. during 2009 and 2016. A newly forming mid-channel bar So many factors control spatially and temporarily like- covering an area of ± 0.42 km² area (as in January, 2016) seasonally varying amount suspended sediment load and and sand deposits can also be noticed along the Kankalmari tidal water discharge, sudden increase in the volume, River and at the confluence of Suia Gang and Matla River velocity and height of the tidal waves during any severe during this period (Fig.3). and varying amount of sediment cyclonic conditions, continuous decrease in downstream load. As the Matla bends and bifurcates through the discharge with high turbidity at identical locations etc. Kankalmari River-Ajmalmari maximum sediment load as control the formation and diminishing of estuarine part or found from the imageries, use to be brought down along the parts of the islands in Indian Sundarbans. The formation of bed of Kankalmari River-Ajmalmari link channel and a new mid-channel bar and sand deposits along the Matla northern part of Ajmalmari island system is very much River around the Ajmalmari islands may not promise to be affected by the erosional works by the Matla River. a stable one to be settled because it may again be eroded at any violent situation like what happened to the New Moore b) The eroded materials mainly borne by the Is. Thus, even if there is unavailability of primary or Kankalmari River which ultimately due to its secondary data we must go through the satellite imagery sluggish flow help in settling down the load along analysis from time to time to identify the changing fluvio- its bed. This process has helped and helping in the geomorphological environment occurring silently in the formation of marsh and swamp in the north-west intra and intertidal zones of the Indian Sundarbans. tip of the Ajmalmari Is. (Fig.3) and helping in the formation of a tiny mangrove island (covering an REFERENCE area of 0.35 km²)and a growing mid-channel bar [1] Bagchi, K. G. (1945). The Gangetic Delta.Calcutta Review, (not formed before 2009). In recent future, if the 1-55. same process persists without any drastic natural change in the upstream and downstream discharge [2] Das, G. K. (2006). Geomorphology. In Sunderbans: and drastic decrease or increase rate of sediment Environment and ecosystem (pp. 38-73). Kolkata-700073, deposition(Gour, 2012) by Matla River in this West Bengal: SARAT BOOK DISTRIBUTORS. intertidal zone of Indian Sundarbans, these islands [3] George, J., Dr, &Chockalingam, J., Dr. (2018). seems to be merged with the eastern part of FUNDAMENTALS OF Remote Sensing (THIRD EDITION Kultali Block around eastern bank of village ed.). Hyderabad, Telangana: Universities Press. Kishorimohanpur.Same conditions are expected [4] Jana, D. (2005). Shrikhanda Sundarban. Deep Prakashan. to occur in the zone between village Baikunthapur Kolkata and Paschim Sripatinagar in Kultali block where [5] O'Malley, L.S.S. (2009). Bengal District Gazetteers: 24- extension of the areal coverage of the marsh or Parganas. New Delhi-110002, New Delhi: Logos Press. swamp is observed during the analysis within the stipulated period (2009-2016). [6] Fluvio-geomorphic Environment of Sunderbans (2005). In S. Kar (Ed.), Sunderbans: PROBLEMS AND PROSPECTS (pp. Epilogue: From the above study and interpretation it can be 59-68). Kolkata, West Bengal: acb publications. opined that temporal formation and washing out of the [7] Retrieved from https://www.lap- point and mid-channel bars are quite common phenomenon. publishing.com/catalog/details//store/gb/book/978-3-8443- But sometimes, some point and mid-channel bars may 1370-3/dynamic-fluvio-geomorphological-environment-of- survive and can give birth of a new tiny mangrove island in indian-sundarbans this deltaic region of Indian Sundarbans. Thus, continuous [8] Sarkar, K. (2007). Itihas Kotha Koy. Gosaba Bazaar, South depositional work have helped in the formation of lots of 24 Parganas, West Bengal: Bhagavati Press. islands in the estuarine parts in earlier times, side by side, frequent shifting of the tidal channels do not create suitable [9] Sengupta, S. (2005).Sundarban: Jib Parimandal (1st ed.). Kolkata, West Bengal: Ananda Publishers Private Limited.

283 | IJREAMV04I0945067 DOI : 10.18231/2454-9150.2018.1190 © 2018, IJREAM All Rights Reserved.